This invention relates to erosion control systems for preventing the erosion of bluffs, dunes and the like located adjacent a body of water, and more specifically to seawalls for preventing such erosion, and to a method for constructing the same.
The erosion of lake or oceanside bluffs represents a serious and longstanding problem. These bluffs are subject to the action of waves pounding against them which erodes away the bluff's base leaving a bluff having a very steep face. This steep front face is very unstable and, in many instances, is unable to support the weight of the dirt, sand, and the like, lying above it. Consequently, landslides may occur, the occurrence of which may endanger cottages or homes built on the top of the bluff.
These bluffs are also subject to the action of hydrostatic forces acting within them. Ground water and water from spray, rain or snow-melt percolates through the bluff, increasing the hydrostatic forces therein. These forces tend to exert an outward pressure against the unstable, steep face of the bluff. Landslides may occur if that outwardly exerted force causes the collapse of the steep face of the bluff.
The percolating water also causes stratification of the sand or soil within the bluff. The strata of soil can slide across each other, decreasing the stability of the bluff itself. This reduction in the stability of the bluff increases the likelihood that landslides will occur.
Structures have been interposed between bluffs and the adjacent body of water in order to prevent the erosion of the base of that bluff and to prevent the occurrence of landslides resulting therefrom. Flat faced seawalls or retaining walls are an example of such prior art structures. However, flat seawalls are relatively inefficient in dissipating the energy of a wave striking against them, and as a result, are plagued by erosion in front of the wall and undermining or tunneling under the wall. Further, it has been recognized that such flat seawalls reflect energy back into the water which accelerates beach erosion rather than promoting beach build-up.
Also, much of the energy of a wave striking a flat seawall is directed downwardly toward the base of the wall. The turbulence associated with this energy results in a trough or tunneling action along the seawall base which undermines the structure, thus causing it to collapse into the water. Moreover, another portion of the wave energy is dissipated by splashing over the top of the wall. This water collects on the bluff and percolates behind the wall, thus increasing the outwardly extending hydrostatic forces within the bluff and eroding the seawall base when it runs back toward the body of water. Such erosion and pressure promotes the failure of the seawall. The problem is exacerbated by rainwater, snow-melt and ground water. In cooler climates heaving of frozen ground behind the seawall and the weight and pressure of ice build-up add to the forces encountered by the wall.
Numerous seawalls have been devised to avoid the deficiencies of flat seawalls. None have been entirely effective. In general, these seawalls have proven to be unstable and eventually subject to collapse from the multitude of forces subjected to the wall.